R-21 missile

The R-21 missile (D-4 complex) is the first in the USSR combat ballistic underwater-launched missile. It could be launched at a force of the sea disturbance up to 5, at a submarine speed up to 4 knots at a depth of 40–50 m. The time to prepare the first missile for launch was about 30 min. The time to launch three missiles was no more than 10 min. Design-layout features of the missile and its launcher, launching from a blind silo without gas ducts made it possible to accommodate the R-21 missile in a smaller silo as compared with the R-13 silo and increase the firing range by about 2.5 fold.